Metals are traditionally applied directly on drawn silica products using a melt of the metal. A small fork, akin to an old-fashioned inkwell pen, or other, similar device, directs or conducts the molten metal to form a bead at the tip, through which the drawn glass passes. In the case of aluminum (used on silica capillary and “specialty” optical fiber”), inert atmosphere is required and adhesion to the silica is rather good. In the case of gold (used on “specialty” optical fiber) adhesion is poor and the fiber is brittle near the ends where atmosphere infiltrates.
Metallization of polymers has also been reported, e.g., polyimides. Generally added as coordination complexes, simple anhydrous or hydrated salts (e.g., silver acetate) to the monomer mixtures prior to polymerization, most of the materials thus formed show unique properties of thermal conductivity, high temperature flexibility, and the like, but lack practicality for applications in drawn processes, due to the strict limitations on polymer “cure” conditions. Thus, there is a need for methods for applying films of gold, platinum, palladium and other metals by reduction of metal ions in organo-metallic compounds in solution to metals, directly on drawn silica, compatible with the conditions in silica draw, with good adhesion.
There is also a need for metal coatings over organic precoats, such as polyimide, which will find applications on silica capillary and fiber for extending use temperature ranges while retaining all of the ease-of-use qualities on plain, polyimide coated capillary. Coaxial electrical and thermal conduction may also find applications, e.g., in sensors.
Finally, metal coated fiber and capillary can be fixed in place with other metals, forming hermetic seals where polymer coated (alone) materials are insufficient.